Understanding Activation Effects on Low-Temperature Biochar for Optimization of Herbicide Sorption

Beatriz Gámiz,Lucia Cox,Kathleen Hall,Kurt A Spokas

doi:10.3390/agronomy9100588

Abstract

Activation treatments are often used as a means of increasing a biochar’s sorption capacity for agrochemical compounds but can also provide valuable insight into sorption mechanisms. This work investigates the effects of H2O2 activation on a low-temperature (350 °C) grape wood biochar, evaluates subsequent changes to the removal efficiency (RE) of cyhalofop and clomazone, and elucidates potential sorption mechanisms. Activation by H2O2 decreased the biochar pH, ash content, and C content. Additionally, the biochar O content and surface area increased following activation, and Fourier transform infrared spectroscopy (FTIR) data suggested a slight increase in surface O groups and a decrease in aliphatic C. Cyhalofop RE significantly increased following activation, while clomazone RE was unchanged. The increased sorption of cyhalofop was attributed to pH effects and charge-based interactions with biochar O moieties. Results from this study suggest that H2O2 activation treatments on low-temperature biochars may improve the removal of organic acid herbicides but are of little value in optimizing the removal of polar, non-ionizable herbicides.

Highlights

There is a growing interest in biochar as sustainable soil amendment due to the agronomical benefits derived from its use
It is unclear whether the bubbling was due to reactions with the carbon structure of the material [28], or the decomposition of H2 O2 catalyzed by metal oxides in the biochar ash component [29], or a combination of the two mechanisms
Because bleaching effects are curtailed by metal-catalyzed degradation of H2 O2 [32], the observed lightening of the biochar itself suggests that the H2 O2 was not solely degraded by metals associated with the ash component

Summary

Introduction

There is a growing interest in biochar as sustainable soil amendment due to the agronomical benefits derived from its use. Biochar has attracted attention for showing sorbent properties towards a wide variety of agrochemical compounds. By binding chemicals such as pesticides, biochar can help prevent and remediate contamination in soil and water [1,2] acting, among others, as a soil ameliorant tool. To further enhance the sorption capacity of biochars, activation processes akin to those used in the production of activated charcoal are increasingly being adopted [3,4] These activation treatments may be useful for improving herbicide sorption capacities of low-temperature biochar (< 400 ◦ C), which are favored for soil fertility applications, but have relatively low sorption capacities. For biochar activation to be effective, it is necessary to understand which biochar physicochemical properties are affected, and whether or not these changes influence the binding of the target compound

Methods

Results

Conclusion